arm: kirkwood: ib62x0: drop CONFIG_MACH_TYPE

Mainline kernel for this device has only support for device tree. We can safely
drop this legacy code.

Signed-off-by: Luka Perkov <luka.perkov@sartura.hr>

include/configs/ib62x0.h

@@ -22,11 +22,6 @@
 #define CONFIG_KW88F6281		/* SOC Name */
 #define CONFIG_SKIP_LOWLEVEL_INIT	/* disable board lowlevel_init */
 
-/*
- * Machine type
- */
-#define CONFIG_MACH_TYPE	MACH_TYPE_NAS6210
-
 /*
  * Enable device tree support
  */